Method of producing a metal film on a refractory base



United States Patent METHOD OF PRODUCING A lVIETAL FILM ON A REFRACTORY BASE Arnold E. Saunders, Jeiferson Township, Butler County, Pan, assignor to Pittsburgh 'Plate Glass Company, Aliegheny County, Pa., a corporation of Pennsylvania No Drawing. Application March 14, 1952, Serial No. 276,680

6 'Claims. '(Cl. 117-227) This invention relates to a method of reducing tin oxide to tin and it has particular relation to a method of reducing a transparent electroconductive tin oxide film on-a refractory base to a tin film on a refractory base.

It is known that transparent electroconductive films may be deposited upon glass by applying stannic chloride to the surface of glass heated above 500 F., preferably 850 to 1350" F. Films of superior conductivity may be produced according to methods described in a copending application for U. S. Letters Patent Serial No. 762,658, filed July 22, 1947, now Patent No. 2,614,944, by William O. Lytle, by spraying plate, window or other glass while it is heated to a temperature of above 500 F., but below the temperature at which the glass becomes molten, with tin tetrachloride or other tin salts in aqueous solution or in vaporstate in the presence of a reducing agent, such as methanol, phenyl hydrazine hydrochloride or other agents. The'films thus obtained are of unknown composition but appear to contain a preponderant amount, of the order of 97 to 99 per cent, of a tin oxide, and certain impurities which may include metallic tin, carbon, silicon, sodium and chlorine and other impurities, depending upon the composition of the applied tin-containing solution.

'These films have a thickness of about 50 to 800 millimicrons, are transparent, and have the unusual characteristic of being electroconductive, the particular degree of electroconductivity being dependent to a large degree upon the nature of the process of depositing the films. Tin oxide films which are deposited in accordance With' the process described above have a resistance below about 500 ohms per unit square, and a specific resistance below about 0.002 ohm centimeters. Further details respecting the production of thesefilms will be supplied hereinafter.

Although articles having such films are useful in many fieldsfthey have been found to be especially useful as Windshields or viewing closures in automobiles, aircraft, trains, and similar automotive vehicles. In such use the coating is placed in series with a source of electric potential, and is used as a heating element in order to heat the closure and prevent deposition of ice, .fog, etc., thereupon. Usually, they are laminated with a suitable plastic,

such as polyvinyl butyral, to reinforce the glass and pro.-

vide' a'so-called .safety glass construction.

It is also known that transparent electroconductive metal oxide films may be produced wherein the film .is composed of other metal oxides in combination with tin oxide or of other metal oxides alone such as cadmium ox-' ide, indium oxide and Zinc oxide or combinations thereof.--

One of the problems in producing transparent electroconductive panels is the provision of satisfactory inexpensive metal strips which serve as bus bars. These metal strips should adhere firmly to the glass sheet, should be in good electrical contact with the transparent electrocon ductive films, and should have conductivity at least 10 to times that of the transparent electroconductive film. It is also desired in the manufacture of certainelectroconductivepanels to provide certain areas of the base;

with a film of higher conductivity than the transparent such as tin oxide film, may be treated to reduce .the tin oxide and to produce an adherent coating of tin metal.

on the glass or refractory baseupon which the tin oxide film may have been deposited. This may be accomplished by subjecting the film or a portion thereof with a metal more electropositive than the metal of the metal oxide film, a non-oxidizing acid and a carbonyl compound such as an aldehyde or ketone or mixture thereof. By carbonyl compound is meant a compound having the group i wherein each of the free carbon bonds are shared by another carbon atom or a'hydrogen atom.

For purposes of determining which metals are more electropositive than the metal of the metal oxide film' such as tin the alkali metals are regarded as being the most electropositive and gold and platinum are regarded.

as being most electronegative metals in the chemical activity series. For example, zinc, cadmium, iron and aluminum are metals which are more electropositive than tin and which may be employed to reduce tin oxide films.

The invention may be practised by simultaneously contacting the tin oxide film or portion thereof with a metal more electropositive than tin, such as zinc, a non-oxidizing acid, such as HCl, and a carbonyl compound such as an aldehyde or ketone or mixture thereof. In order to clearly define terms, an oxidizing acid as described herein refers to an acid that does release hydrogen upon reaction with a metal of the class utilized hereinafter to reduce a metallic oxide coating to a metallic coating whereas a non-oxidizing acid reacts with a metal of the same class to form hydrogen and the metal salt containing the acid radical. I v

A further embodiment of the i invention comprises depositing a pulverulent metal which is more electropositive than tin such as zinc togetherwith a dispersing agent and a water dispersible binder which'serves as a binding medium to hold the zinc on the base, upon the tin oxide film or portion thereof to be reduced; Thereafter, the zinc or other metal fcoating maybe sprayed 'or otherwise coated with an aqueous solution of a non-oxidizingacid and a.

pound such as an aldehyde or ketone or mixture thereof: and thereafter contacted with a block or pencil of zinc- Such method is'especially appli-- or equivalent metal. cable when only specified areas of the tin oxide are desired to be reduced to tin. Other methods whereby the tin oxide film is contacted simultaneously with the electropositive metal, a non-oxidizing acid and a carbonyl compound may be used according to this invention.

A shiny tin film is produced in the areas of the trans-" parent electroconductive tin oxide film thus treated. The transparent electroconductive oxide film may be thustreated along opposingedges ofrthe refractory base to;

Patented Sept. 11,1956

form-thin tin strips along" such edges which may be reinforced by. suitable metahsuch. ascopperte formsatisfactory bus bars. The tin film thus formed has a thickness of about 50 to 800 millimicrons, and a resistivity of fromlessthan 1. ohm to 50'to 1.00 ohms'per square. Thetin film thus producedmay be thickened byelectrode'position, dipping, cathodesputtering oriotherdevice.

The shiny tin film produced on a refractory base in accordance with this invention is' capable o'f'many uses. It may be used as a front surface mirror; In addition it may be used as a base to which other metals may be soldered or otherwise connected to form an-adherent glass to metal seal. which is desirable inthe ma'nufa'cture of many commercial products such as television tubesand double glazed windows.

The following. example illustrates the manner in which a: transparent electroconductive tin oxide film. may be reduced to a tin film in. accordance. with the invention. Example 1 A piece of lime-soda plate glass 6 inches by 6 inches by inch was placed in a furnace and heated at a furnace temperature of 1050" F. for about 3 minutes. ately after this, the heated base was removed from the furnace and sprayed with 10 cubic centimeters of a solution composed of the following ingredients:

Stannic chloride -grams 20,430 Phenylhydrazene hydrochloride do 639 An. aqueous solution of hydrofluoric acid do 134 Distilled water milli1iters 7,056 Dioctyl sodium sulfosuccinate solution do 918 Methanol .do 2,250

A clear transparent electroconductive tin oxide film havinga resistance of about 50 to 125 ohms per unit square was obtained.

A slurry of pulverulent powdered zinc was applied to the base. The slurrywas prepared in the following mannot:

solution was mixed in equal parts by volume with methanol, and one pound of powdered zinc was then added per quart of the resulting methanol solution. About 5 cubic centimeters of the solution thus obtained wasthen applied to the coated base to deposit a thinzincclontai'ning film upon the surface thereof and allowed to About 25 milliliters ofa solution made up in the proportion of 1 gram of acetone and 10 grams of' an aqueous" solution of 1.5 normal hydrochloric acid was then applied to the Zinc coating. An adhering layer of bright tin metal. was formed in the areas. coated with the zinc and the acid=acetone solution. The tin film had a resistivi'ty or 3 ohms per unit square.

The amount of zinc or other electropositive metal which should be employed per square centimeter of metal oxide film depends upon the thickness of film to be reduced. For example, the amount of zinc which should be employed to reduce a layer of tin oxide film of about 100 millimicrons thickness is about 0.001 gram per square centimeter or more depending upon any tendency of the zinc to float or otherwise move off the tin oxide film before acting upon it.

Thus it can be se'en, for example, that when a tin oxide film; of 400 millimicrons thickness is' treated with only sufiicient zinc, no'noxidizing acid and carbonyl compound to'- reduce alayer 200 millim'icrons in thickness, that there still remains intermediate the" tin fibln' and the refractory Immedi-' base, a layer of tin oxide film which is tightly adherent to therefractory base.

It appears that the metal film is slightly more adherent when a thin layer of the metal oxide film is allowed to remain on the base. The terminology in the claims relating to a tin or metal film on a. refractory base are intended to include those tin or metal films that are produced by reducing all or only a portion of the thickness of the metal oxide film.

The following example illustrates a method whereby only a certain thickness of. a tin oxidefilmon arefractory base is reduced to an adherent tin film.

Example II A piece of lime-soda plate glass 6 inches by 6 inches by W inch containing a transparent electroconductive tin oxide film is coated with a zinc coating as in Example I with the exception that only /5 pound of .zinc is:mixed with the methanol solution.

The zinc coated base is treated as in Example with the solution made up of acetone and hydrochloric acid and an adhering layer of bright tin metal is formed inv the areas treated with the zinc and acid-acetone solution. By turningthe treated plate over, the presence of. a. tin oxide coating adjacent the glass and in between the glass and tinmetal layer can be observed due to the difference in the color of the film as produced by reflected light.

Various aldehydes and ketoncs were use in conjunction with. zinc and a dilute non-oxidizing acid to test their ability to reduce atin oxide film to a tin film. The aldehydes and ketones were tested in the same manner as shown in the example above. The following aldehydes may be employed: formaldehyde, acetaldehyde, chloral, glyoxal, propionaldehyde, n butyraldehyde, n-valeraldehyde, n-caproaldehyde, n-heptaldehyde, acrolein, crotonaldehyde, benzaldehyde, chlorobenzaldehyde, nitrobenzaldehyde, tolualdehyde and furfuraL.

In addition to acetone, other ketones whichmay be.

used in the practice of the invention include methyl ethylv ketone, methyl. n-propyl ketone, diethyl ketone, hexanone-Z, hexanone-3, methyl t-butyl ketone, di-n-propyl ketone, diisopropyl ketone, diisobutyl ketone, di-n-amyl ketone, stearone, chloroacetone, acetylacetone, mesityloxide, phorone, cyclohexanone, acetophenone, propiophenone and benzophenone.

Other carbonyl compounds which have been found to be suitable in the practice of the invention are. carbohydrates including sugars and mixtures thereof. For example, a mixture of levulose and dextrose has been found to reduce a tin oxide film to a' tin film where contacted with the tin oxide film in the presence ofzinc and anonoxidizing acid. For purposes of describing and claiming: the invention, the sugars such as fructose, dextrose and.

levulose and mixtures thereof are considered as being included in the terms aldehyde and ketone;

Variousacids may be used in lieu of dilute aqueous solutions of hydrochloric acid; for example, hydrobromic' acid, sulfuric acid, phosphoric acid, phosphorousv or sulphurous: acid, or other mineral acid or equivalent. acid.

which does not readily etch glass and in which. the anion thereof is. essentially non-oxidizing in character. The concentration of the acid used normally is within 0.5 to 10 per cent by weight. of the aqueous solution although other solutions could be used. The amount of acid. used in conjunction with the above described car bonyl compounds is capable of some variation. These should be suflicient to thoroughly wet the zinc coated surface. An excess of acid will not be harmful provided the proper amount of carbonyl compound is present.

Generally it. is desired in order to achieve reduction ofthe tin oxide film to a layer of tin in accordance with this invention, that about one mole of a carbonyl compound as enumerated above be applied in combination with about 0.5 to 10 equivalents of one of the acidsset forth above. If too large an amount or a carbonylcompound isobutyraldehyd'e,

dichloroacetone', diacetyl,

with respect to the acid is employed, there will be substantially no reduction of the tin oxide. On the other hand, if too small an amount of a carbonyl compound with respect to the acid is used, the tin oxide will go into solution and no appreciable amount of tin will be formed.

The invention is particularly applicable for use in con nection with the reduction of a transparent electroconductive tin oxide film to an adherent tin film. However the invention is also applicable in connection with the reduction of tin oxide and other metal oxides in combination in the same film such as films containing a major amount, at least 70 to 80 per cent by weight of tin oxide with minor amounts of the oxides of antimony, copper, zinc, thallium, vanadium, chromium, manganese, cobalt, cadmium, indium and/ or titanium.

Furthermore, the invention may be practiced with regard to the reduction of other metal oxide films to produce metal films on a refractory base such as cadmium oxide, zinc oxide, indium oxide, etc. and various combinations thereof as described above with respect to tin which may be prepared by contacting a heated refractory base with the bromide, chloride or acetate of the corresponding metal or mixture thereof.

Where viewing closures for vehicles are to be provided, the base for the film normally is ordinary soda lime glass. Other refractory materials including borosilicate glass, china, mica, phosphate glass, silicon carbide, tungsten carbide, porcelain, stone or other refractory composition which melts at temperatures above 1150 to 1350 F. may be provided with metal films in accordance with this invention.

Although the present invention has been described with reference to the specific details of certain embodiments thereof, it is not intended that such details shall be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims.

What is claimed:

1. A method of producing a metal film on a refractory base having a metal oxide film of the class consisting of tin oxide, cadmium oxide, indium oxide, zinc oxide, combinations thereof, and films containing at least 70 to 80% by weight of tin oxide combined with minor amounts of at least one oxide from the group consisting of the oxide of antimony, copper, thallium, vanadium, chromium manganese, cobalt and titanium, thereon, which comprises subjecting the metal oxide film to the action of a metal, an aqueous acid solution of a carbonyl compound, said metal taken from the class of metals more electropositive than the metal of the metal oxide film consisting of zinc, cadmium, iron and aluminum, and said acid taken from the class consisting of hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, phorphorous acid, and sulfurous acid, the proportions of said acid and carbonyl compound being from 0.5 to 10 mol equivalents of acid to each mol of carbonyl compound.

2. The method according to claim 1 wherein the acid is applied in the form of an aqueous solution containing from 0.5 to 10% by weight of the acid.

3. A method of producing a tin film on a refractory base having a tin oxide film, which comprises subjecting the tin oxide film to the action of a metal, an aqueous acid solution and a carbonyl compound, said metal taken from the class of metals more electropositive than tin consisting of zinc, cadmium, iron and aluminum, and said acid taken from the class consisting of hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, phosphorous acid, and sulfurous acid, the proportions of said acid and carbonyl compound being from 0.5 to 10 mol equivalents of acid to each mol of carbonyl compound.

4. The method according to claim 3 wherein the acid is applied in the form of an aqueous solution containing from 0.5 to 10% by weight of the acid.

5. A method of producing a tin film on a refractory base coated with a tin oxide film, comprising contacting the film with a mixture of Zinc, an aqueous acid solution and a carbonyl compound, said carbonyl compound selected from the class consisting of aldehydes, ketones, and mixtures thereof, and the acid selected from the class consisting of hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, phosphorous acid, and sulfurous acid, the proportions of said acid and carbonyl compound being from 0.5 to 10 mol of acid to each mol of carbonyl compound.

6. A method of producing a tin film on a refractory base coated with a tin oxide film which comprises depositing pulverulent zinc upon the tin oxide film and thereafter applying to the zinc an aqueous solution of an acid and a carbonyl compound, saidacid taken from the class consisting of hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, phosphorous acid, and sulfurous acid and said carbonyl compound selected from the class consisting of aldehydes and ketones and mixtures thereof, the proportions of said acid and carbonyl compound being from 0.5 to 10 mol equivalents of acid to each mol of carbonyl compound.

No references cited. 

1. A METHOD OF PRODUCING A METAL FILM ON A REFRACTORY BASE HAVING A METAL OXIDE FILM OF THE CLASS CONSISTING OF TIN OXIDE, CADMIUM OXIDE, INDIUM OXIDE, ZINC OXIDE, COMBINATIONS THEREOF, AND FILMS CONTAINING AT LEAST 70 TO 80% BY WEIGHT OF TIN OXIDE COMBINED WITH MINOR AMOUNTS OF AT LEAST ONE OXIDE FROM THE GROUP CONSISTING OF THE OXIDE OF ANTIMONY, COPPER, THALLIUM, VANADIUM, CHROMIUM MANGANESE, COBALT AND TITANIUM, THEREON, WHICH COMPRISES SUBJECTING THE METAL OXIDE FILM TO THE ACTION OF A METAL, AN AQUEOUS ACID SOLUTION OF A CARBONYL COMPOUND, SAID METAL TAKEN FROM THE CLASS OF METALS MORE ELECTROPOSITIVE THAN THE METAL OF THE METAL OXIDE FILM CONSISTING OF ZINC, CADMIUM, IRON AND ALUMINUM, AND SAID ACID TAKEN FROM THE CLASS CONSISTING OF HYDROCHLORIC ACID, HYDROBROMIC ACID, SULFURIC ACID, PHOSPHORIC ACID, PHOSPHOROUS ACID, AND SULFUROUS ACID, THE PROPORTIONS OF SAID ACID AND CARBONYL COMPOUND BEING FROM 0.5 TO 10 MOL EQUIVALENTS OF ACID TO EACH MOL OF CARBONYL COMPOUND. 